[Study of GCN repeats of PHOX2B gene among individuals from southwest China and diagnosis of two patients with Congenital central hypoventilation syndrome].

OBJECTIVE: To study the trinucleotide repeats of GCN (GCA, GCT, GCC, GCG) encoding Alanine in exon 3 of the PHOX2B gene among healthy individuals from southwest China and two patients with Congenital central hypoventilation syndrome (CCHS). METHODS: The number and sequence of the GCN repeats of the PHOX2B gene were analyzed by capillary electrophoresis, Sanger sequencing and cloning sequencing of 518 healthy individuals and two newborns with CCHS, respectively. RESULTS: Among the 1036 alleles of the 518 healthy individuals, five alleles were identified, including (GCN)7, (GCN)13, (GCN)14, (GCN)15 and (GCN)20. The frequency of the (GCN)20 allele was the highest (94.79%). And five genotypes were identified, which included (GCN)7/(GCN)20, (GCN)13/(GCN)20, (GCN)14/(GCN)20, (GCN)15/(GCN)20, (GCN)20/(GCN)20. The homozygous genotypes were all (GCN)20/(GCN)20, and the carrier rate was 89.58%. Four GCN sequences of the (GCN)20 homozygous genotypes were identified among the 464 healthy individuals. The GCN repeat numbers in the exon 3 of the PHOX2B gene showed no significant difference between the expected and observed values, and had fulfilled the,Hardy-Weinberg equilibrium. The genotypes of the two CCHS patients were (GCN)20/(GCN)25 and (GCN)20/(GCN)30, respectively. CONCLUSION: It is important to determine the GCN repeats and genotypic data of the exon 3 of the PHOX2B gene among the healthy individuals. The number of GCN repeats in 518 healthy individuals was all below 20. The selection of appropriate methods can accurately detect the polyalanine repeat mutations (PARMs) of the PHOX2B gene, which is conducive to the early diagnosis, intervention and treatment of CCHS.

Prenatal diagnosis of mosaic chromosomal aneuploidy and uniparental disomy and clinical outcomes evaluation of four fetuses.

BACKGROUND: Few co-occurrence cases of mosaic aneuploidy and uniparental disomy (UPD) chromosomes have been reported in prenatal periods. It is a big challenge for us to predict fetal clinical outcomes with these chromosome abnormalities because of their highly heterogeneous clinical manifestations and limited phenotype attainable by ultrasound. METHODS: Amniotic fluid samples were collected from four cases. Karyotype, chromosome microarray analysis, short tandem repeats, and whole exome sequencing were adopted to analyze fetal chromosomal aneuploidy, UPD, and gene variation. Meanwhile, CNVseq analysis proceeded for cultured and uncultured amniocytes in case 2 and case 4 and MS-MLPA for chr11 and chr15 in case 3. RESULTS: All four fetuses showed mosaic chromosomal aneuploidy and UPD simultaneously. The results were: Case 1: T2(7%) and UPD(2)mat(12%). Case 2: T15(60%) and UPD(15)mat(40%). Case 3: 45,X(13%) and genome-wide paternal UPD(20%). Case 4: <10% of T20 and > 90% UPD(20)mat in uncultured amniocyte. By analyzing their formation mechanism of mosaic chromosomal aneuploidy and UPD, at least two adverse genetic events happened during their meiosis and mitosis. The fetus of case 1 presented a benign with a normal intrauterine phenotype, consistent with a low proportion of trisomy cells. However, the other three fetuses had adverse pregnancy outcomes, resulting from the UPD chromosomes with imprinted regions involved or a higher level of mosaic aneuploidy. CONCLUSION: UPD is often present with mosaic aneuploidy. It is necessary to analyze them simultaneously using a whole battery of analyses for these cases when their chromosomes with imprinted regions are involved or known carriers of a recessive allele. Fetal clinical outcomes were related to the affected chromosomes aneuploidy and UPD, mosaic levels and tissues, methylation status, and homozygous variation of recessive genes on the UPD chromosome. Genetic counseling for pregnant women with such fetuses is crucial to make informed choices.